Technical Abstract: Switchgrass (Panicum virgatum L.) is a warm-season (C4) perennial grass and a potential bioenergy crop. On-farm switchgrass field scale trials, which were initiated to obtain economic production information for switchgrass grown as a bioenergy crop in the Northern Plains, provided field sites to determine the relationships between establishment year stand and post-establishment year stands and biomass yields both within and across fields. An additional objective was to determine if a stand threshold exists for switchgrass grown as a biomass energy crop at the field scale. Switchgrass was seeded in 10 cropland fields, ranging in size from 3 to 9.5 ha, in Nebraska, South Dakota, and North Dakota in 2000 and 2001. The fields were selected to be representative of their region and be eligible for the Conservation Reserve Program. Twelve sites within each field were geo-referenced, and switchgrass stand frequency was measured at each sample site. Biomass yields were estimated in late summer at the same within field sites using a clipped quadrat. Fields with low initial switchgrass stand frequencies showed a linear relationship between initial stands and second year switchgrass stands and biomass yields. Results from the three-state evaluation area indicate that an establishment year stand frequency levels of 40% or greater as determined by a frequency grid can be considered an establishment year stand threshold for successful establishment and subsequent post-planting year biomass yields for switchgrass grown as a bioenergy crop in the Northern Great Plains, USA. An establishment year stand frequency of 25% would be adequate for a switchgrass conservation planting for which no harvests would be planned for several years.